Sneezes Travel Even Farther Than We Thought

FROM “VIOLENT EXPIRATORY EVENTS: ON COUGHING AND SNEEZING,” BY LYDIA BOUROUIBA, ELINE DEHANDSCHOEWERCKER AND JOHN W. M. BUSH, IN JOURNAL OF FLUID MECHANICS, VOL. 745; April 2014

This cloud has nothing to do with the weather. It's a cloud of snot, and when propelled by a sneeze, it can carry droplets 200 times farther than experts previously thought, according to research published in the Journal of Fluid Mechanics.

After filming people coughing and sneezing at high speed, mathematicians and engineers at the Massachusetts Institute of Technology ran mathematical models and simulations to investigate the cloud's role. Approaching the violent respiratory event from a fluid mechanics perspective, the researchers found that some previous assumptions about sneezes were wrong. The largest mucus and spittle particles, for example, do not travel the farthest, even though that is what momentum would predict. Unexpectedly, the tiniest droplets all interact with the gas instead of operating individually. Caught up in the cloud, they behave more like a whiff of smoke than the spray of a garden hose. As a result, whereas the large droplets travel up to four feet, the small droplets can reach eight feet.

This finding may be fundamental to our ability to control the spread of disease. A gaseous cloud of hitchhiking microbes could travel far enough to reach ventilation units, meaning its dispersal potential is much greater than had been assumed. The work could help researchers estimate the disease-spreading potential of various air conditioners and map how pathogens may ultimately float around an office, airplane or home.